Battery issue

“nothing works ” lights? water pump?

It may be that the battery disconnect switch ("salesman switch") is set to the disconnect state. If so, cycle it on and things should work better. Often this switch is near the entrance door, and it's usually a sort of momentary toggle: press one side briefly to switch it on, the other side to switch it off, with a latching relay that does the actual switching somewhere in the guts of the RV.

If yuou have an inverter, there should be a fuse close to the batteries in the lead to the inverter. Check that this fuse is not blown. Warning - it may not be in a logical place.

Year brand model of RV

Perhaps you only have a "converter" that charges the batteries from 120vac
Not an "inverter" that makes 120v from battery power

Many RVs never had an inverter option for making 120v from battery power, if you do not have a built in generator, it is unlikely you have an inverter, generator was a much more popular option

Your lights water pump , heater/furnace.. Should work without 120v
Those are 12v from the camper house battery, not the engine/chassis battery

Even the fridge uses 12v for control circuits, even when operating on propane, which is the most efficient way, and the only way when there is no shore power plug in